Sharif Digital Repository

The subject of this study is design of a linear quadratic Gaussian controller based on identification of dynamic behavior of unmanned model helicopter “Raptor” in its hover flight. To achieve this end, first, the helicopter linear transfer functions are identified with frequency response method by applying specific inputs to the model of Raptor in the X-Plane software and receiving system outputs via Simulink. Next, using the identified dynamic model of the helicopter, an optimum linear controller is designed for hover flight. As an optimum linear controller needs all the state variables, a Kalman filter is utilized to estimate them, using outputs of various sonsors such as GPS and gyro.... 

According to modal interpretations of quantum mechanics, a state possesses definite values even if it is not an eigenstate. On the other hand, Kochen-Specker theorem holds that all possible possessed values by a system can not be definite. Consequently, modal interpretations to block this theorem, take new metaphysics of properties. In this dissertation, I will show that dispositionalism is that metaphysics. According to dispositionalism, causal powers of a property are constituents of the property. As regards this outline, the thesis would be divided into 5 chapters. In chapter one, presuppositions of later arguments are clarified. Chapter two is related to algebra of properties and finally... 

Density currents, caused by the intrusion of dense fluids under lighter ambient fluids, frequently occur in both natural and industrial situations. As a result of the density differences, the driving force can arise from soluble substances, temperature differences, etc. If the driving force comes from suspended particles including silt and mud, the currents are called turbidity currents. Due to the variation in concentration and the consequent driving force along the flow path, turbidity currents are significantly more complicated than saline currents. These currents play the most important role in sedimentation in lakes, seas and oceans. In addition, turbidity currents are the main factor... 

In this thesis, dynamics of a turbojet’s fuel control unit is studied for the nature and the range of its inputs and outputs. Then, inputs and outputs involved in the system identification process are determined. Tools needed for the application of the input and the signal data sampling are recognized, and henceforth, with the appropriate input applied and the frequency-domain system identification process carried out, desired linear transformation functions representing dynamics of the fuel control unit are found. Using these transformation functions, the fuel control unit is simulated to be converted to an electronic control unit  

Along with the emergence of the smart city concept and the increasing demand for a wide range of vehicles, the Internet of Vehicles (IoV) has attracted a lot of attention by providing numerous benefits including vehicle accident warning, reducing pollution levels and traffic congestion, as well as entertainment services. Furthermore, IoV offers various services combining Vehicular ad hoc networks (VANETs) and IoT in smart cities. However, these types of networks are exposed to a variety of security and privacy risks due to the wireless nature, because the sensitive message is transmitted through an insecure channel in the IoV-based smart city environment, therefore, it is necessary to... 

Delay Tolerant Networks are types of mobile Ad-hoc networks, in where because of the high node mobility, low node density and node diversity, there is not full connection between nodes in the whole network; therefore, the probability of existence of end-to-end path between source and destination is low. Due to these properties, message routing in delay tolerant networks has turned to be a challenge, this type of networks work based on the concept of store, carry, forward; for instance, a node may store a message in the buffer for a long time and carry it along until meeting an appropriate contact opportunity. Delay tolerant networks are capable of providing communication services in... 

With the growing development of the aviation industry, the emitted jet noise from civil and military aircraft has become a challenging issue in the development of this industry. Despite recent advances in simulation methods using for fluid phenomena, understanding the nature and physics of noise generated by jet flows has been a complex puzzle for the last decades. Although numerical methods are currently able to predict the jet noise, it is still not possible to fully understand the physics of this phenomenon and subsequently use it to control the emitted sound. In this research, with the purpose of studying the pressure fluctuation caused by large-scale coherent turbulence structures in... 

The purpose of this research is to investigate the residual stresses generates during solidification of a casting part and the effect of casting geometry and thermal treatment conditions on these stresses. The pattern was designed with to arms to ensure tensile tension. CO2 process was used for modeling and due to the high hardness of the mold, it also acts as a constraint and exacerbates the tension. To measure tensions in parts, two methods consist of Hole Drilling, and an innovative method based on heat treatment and dimension change have been used. The results of the two methods show the same values of stress. The Hole Drilling method is a verified and high-precision method, which is... 

While the population of the cities all over the world is increasing, more and more tunnels and underground transportation passages are being constructed. So, there is an urgent need for designing an appropriate ventilation system for these passages, not only in normal conditions but also for emergency scenarios especially in fire incidents.In the present research, the operation of Saccardo ventilation system, especially in emergency fire scenarios is investigated using computational fluid dynamics methods. Studies conducted in this research are classified into five parts.In the first part, the effect of tunnel ventilation flow rate (due to Saccardo system operation) and its interaction with... 

Uranium is the most important element in the nuclear fuel cycle. Recovery of uranium from waste produced at every stage of the fuel cycle is not only economically important, but also environmentally important. In the production phase of uranium hexafluoride, certain amount of solid waste is produced in the bottom of the fluorination reactor. In order to extract the uranium from this waste, we have to eliminate the fluorine contained in the waste. This is because the fluorine forms strong complex with uranyl ions during the extraction process, and prevents from efficient extraction of uranium. In the current thesis؛ first, we examined the characteristics of the waste ... 

Chaos is defined as an unpredictable and unrepeatable motion which has been observed in many classical systems such as unharmonic oscillators and turbulent currents in fluids. The common aspect of these types of motions is the deterministic nonlinear equation. On the other hand, quantum mechanics is a stochastic theory which is based on probabilistic description of quantum systems. These approaches lead to quantum chaos phenomenon which has been a controversial issue in the recent years. In the thesis, by studying the classical chaotic models such as kicked rotor, billiard model, excited hydrogen atom under microwave field and etc, we examine the existence of chaotic behavior in quantum... 

Designing Nonautonomous periodic systems such as helicopters, multirotors, monocopters or the dynamics of flapping wings requires stability analysis and careful examination in order to identify and determine their dynamic behaviour. In practice, analysis and design are interdependent and the design of nonlinear control systems involves an iterative process. To know the importance of identifying and to accurately implement methods to analyse this kind of systems in the field of aerospace, the flapping wing can be a good example. The issue of stability and the control of the flapping wings have not yet had a clear solution, and the current research including controller design based on linear... 

According to the impossible trinity, countries can only enjoy from two of the following choices simultaneously: fixed exchange rate, free capital flow and independent monetary policy. A part of the economics literature has tried to verify the theory empirically. Some of the researches like Klein and Shambugh(2015) has concluded that the trilemma is valid on the occasion of transferring the effect of base countries interest rate changes to other countries. On the other side, a few papers like Ray(2013) has shown that an independent monetary policy can just be obtained by a closed capital flow and a float exchange rate system can not necessarily give central banks the autonomy of monetary... 

Undoubtedly, the concept of information has an outstanding role in our description of physical systems and biological processes. In the framework of pragmatic approach, information is a useful notion through which any physical event gets its significance. In this approach, information can be understood and recognized while it is capable of producing new information. Thus, the meaning of information depends on our recognition and understanding as conscious beings. Accordingly, the following question may arise: where is the role of conscious being in the emergence of physical properties in Nature? To answer this fundamental question, we first investigate how information enters the physics, in... 

Reducing energy consumption is one of the challenges facing wireless sensor networks with many solutions introduced for them with each having advantages and disadvantages. Some of the solutions introduced are based on using movable sinks. In this project, we attempt at proposing a place for the establishment of sinks using genetic algorithm that can reduce energy consumption in the net knots and increase the net life. This work should be done after reviewing the results of past researches and introduced methods. We will analyze the practicality of the proposed model using simulation and will show their advantages over the previous mentioned methods  

Reusing third-party libraries is inevitable to reach an acceptable development time and cost in current application development methodologies. As these libraries are placed in the address space of the native application, they have the same access rights as it.These libraries may contain deliberate or unintended bugs that result in security vulnerabilities.Previous approaches to limit access rights of these libraries either lack a comprehensive control over different resources, e.g., they prevent unprivileged access to RAM while illegal disk or network access is still possible, or impose significant performance overhead.In this thesis, we have presented a secure approach to third-party... 

Direct reduction of iron is a process to reduce iron in solid phase. The output of this procedure is direct reduced iron (DRI) that can be used in electric arc furnacewithout further changes. Midrex technology, which is the most important one among direct reduction of iron processes, provides 60% of DRI.
Required synthesis gas for reduction process is gained from reforming of the natural gas,with the major proportion of methane, with water steam and carbon dioxide in a piece of equipment called “reformer”. As a matter of fact, reformer is a type of plug chemical reactors. Input materials (natural gas, water steam and carbon dioxide) enter from the bottom section to the prepared pipes in... 

Vehicular ad hoc networks (VANETs) can prepare scalable and cost effective solutions for applications such as traffic monitoring and vehicle safety. However, VANETs often experience congestion quicker than wired networks, leading to high end to end delay. The optimization method was proposed to improve the end to end delay of Ad-hoc On-demand Distance Vector (AODV) routing protocol in VANETs. It was shown that Last-In-First-Out with FrontDrop (LIFO-FD) queuing system for AODV routing protocol performs better in high traffic periods in term of end to end delay. The simulation studies were performed on the impact of queuing systems on end to end delay of AODV routing protocol in VANETs. The... 

In recent years, due to fires in mines around the world, the need to study the dynamic behavior of fire to understand how it spreads and design an appropriate fire extinguishing system to reduce damage to people and underground facilities has been felt. Mine fires are usually caused by external sources such as cable connections, methane gas explosions, or coal self-ignition due to oxygen uptake and rising temperatures.In this research, using Fire Dynamic Simulator (FDS) software, after drawing the geometry of a coal tunnel corridor in progress and creating a fire model through pyrolysis of PVC, fire extinguishing was performed by nozzles. If the nozzle does not succeed in extinguishing the... 

The widely used services such as search engines, websites and social networks are deployed on multiple servers for quick and reliable access. Therefore, there is need to load balancer for distributing requests. In traditional networks usually dedicated hardware load balancers are used, which are very expensive, inflexible, single point of failure and prone to congestion. To solve this problem, using software defined networks, a simple device which works based on OpenFlow protocol can turn into a powerful load balancer with installing the rules by the controller.In software defined networks, a controller is used for load balancing, which has two main problems. First, in case of a failure in...